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Competition
•• CompetitionCompetition–– Two species use the same limited Two species use the same limited
resource resource oror harm one another while harm one another while seeking a resourceseeking a resource
–– Resource CompetitionResource Competition–– Interference CompetitionInterference Competition
Competition• Resource Competition
– Organisms use common resources that are in short supply
Competition• Interference Competition
– Organisms seeking a resource harm one another in the process, even if resource is not in short supply
Competition• Long history in ecology
• Competitive exclusion principle: Complete competitors cannot coexist– Leads to specialization
Competition• N. American ungulates tend to be
generalists…
• flexible in habitat use and feeding?
• Why?– Pleistocene extinction 12,000 – 15,000
years ago most large mammals went extinct…..
Competition
• Page 66, Bailey 1984
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Competition
• Page 66 from Bailey 1984
Competition
• Would you expect competition among these species?
• Which ones and under what conditions?
Competition
• Even though species occupy different niches, enough overlap for competition– Contemporary examples?– How would you know if competition is
occurring?
• Examine diet overlap– Study of ungulates in the Texas Hill
Country
Competition
• Tables 1 and 2 from Henke et al. JWM 52:595-598
Competition
• Another way is to look at several niche dimensions. If a lot of overlap, then competition is possible….
Isle and Hellgren 1995 J. Mammalogy 76:784-799
Competition
• Bedding sites also different– Pigs bedded on edge of mottes with better visibility– Peccaries bedded in thick vegetation with low visibility
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Competition• On Chaparral WMA (JWM 65:99-110)
– Pigs used more open areas; less selective in placement of HR because HR was large
– Peccaries favored dense woody vegetation and were more selective in HR placement
– Pigs used open areas, peccaries used thick vegetation with more cactus
– Temporal – day vs. night habitat use
Competition• Competition understood best through
manipulative experiments
• Expensive to conduct, will see data later
Competition• Livestock – Wildlife Competition??
Competition• Livestock – Wildlife Competition
– Important because both wildlife and livestock have value that people wish to capture
• Different from wildlife--wildlife – Livestock densities above sustainable– Not subject to density dependent controls– Artificial feed, water and removed if range
conditions become bad
Competition• Impacts of livestock on wildlife• Direct – resource and interference
competition that we have discussed• Indirect (esp. if grazing pressure is high)
– Reduction in plant vigor– Lower reproduction by plants– Changes in vegetation cover types– Changes in plant species composition– Change habitat use & movements of wildlife
Competition• Operational impacts
– Species of livestock– Grazing regime (timing and duration)– Fencing– Water development– Range alteration (e.g. brush control)– Predator-prey relations altered– Disturbance from management activity – Disease
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Competition• White-tailed deer in general
– Least likely to compete with cattle– Compete with sheep for forbs– Compete with goats for browse
• Wet years – deer preferred– cattle > goats > sheep
• Dry years – deer preferred– cattle > sheep > goats
• Avoided pastures w/ livestock• Survival and natality lower w/ livestock
Competition• Study of cattle-deer competition in western
Colorado (Ecological Applications 6:200-227)
– Elk winter ground, cattle summer grazing
• Positive effects of elk– Removed dead grass, cattle diets better quality
• Negative effects of elk– Forage biomass was reduced
Competition
• Higher diet quality was not enough to make up for reduced intake rate
– Lower calf production in pastures grazed by elk– Dead grass was important as a buffer in this
arid system– Elk grazing reduced this buffer
Competition
• Lessons for wildlife management:– Well managed grazing may serve as a tool in
deer management by removing grass and promoting growth of forbs
– In Great Basin, livestock grazing reduced fires and promoted shrub growth. Benefited mule deer whose populations increased through the mid 1900s
Intraspecies competition?
• Males and females live in different habitats or use habitats differently…. Why??
• Predators?• Avoid competition?• Different food quality requirements?
Sexual Segregation
• Larger-bodied males eat abundant, high-fiber forage– Rumen capacity = prolongs
retention time– Able to use fiber for energy
• Females smaller-bodied, but requirements change– Better post-rumen digestion
and nutrient absorption– Digestive tract changes
Barboza and Bowyer 2000
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Predation
• Views of predators have changed
• Considered competitors & dangerous– Early form of game management– Military shot predators in YNP soon after it was
established
• 1930s – different view emerges– Leopold watches wolf die– Errington proposes “doomed surplus”
Predators in South Texas• Original predators: Wolves Lions Jaguars Bears Coyotes Bobcat And people!
• Now….
Timing of fawn deaths
Vreeland (2002) – 218 fawns
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18
14
728%
12.0%4.3%
59.2%23.3%
18.0%
47.9%54.0%
12.7%
20.4%24.7%
27.6%
1.9%19.4%
27.0%10.3%
73.0%
What kind of coyote predationrates have been reported?
Predation
• Predation effects are complex• Predators limit prey in some situations
• How can we determine predator effects? Mortality sources Manipulated systems Manipulative studies
Predation
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• Figs. 1 and 2 from JWM 38:857
Predation Predation
• Welder Refuge:
coyotes & bobcats
361 ha enclosure for 7 years
Predation Predation
• Lions S Texas: 49% (37 of 75) lion kills = deer 58 bucks marked near Freer in late ’80’s
• 15 deaths• 2 killed by lions
• Bobcats Scats at Welder
• Deer hair May-Aug, peaks in June• Adult deer rarely taken
Predation
• Coyotes 81 fawns collared in 60’s
• 58 died, 29 = coyote
Freer study, 58 adult bucks• 3 deaths where coyote was probable
Heffelfinger study, 3 yrs, 97 bucks• 8 deaths, 3 where blood, signs of struggle
Predation
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Predation Predation
• Vulnerability of prey Habitat quality
Animal quality• Poor quality animals more susceptible to predation
Buffer species
Predator evasion strategy• Not effective against all predators
Role of predators not appreciated until recently
Consider Aldo Leopold’s changing views on wolves and predators in general……
Predators are part of the system So what’s the bottom line…
In productive deer herds, coyote predation may not be a significant factor
You must consider coyote predation in the context of your deer herd conditions!
So what’s the bottom line…
In low-productivity herds, coyote predation may limit the number of does that can be harvested.
Either must increase productivity, or reduce mortality (control?).
How to limit coyote
predation?
Consider the habitat…
Cover!
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South Texas is a place of contrastsSouth Texas is a place of contrasts South Texas is a place of contrastsSouth Texas is a place of contrasts
Grazing management = cover management
Grazing management = cover managementRain: the great equalizer
Abundant forage for lactating doesPlenty of cover for fawns
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Drought: the real fawn-killer
Poor forage for lactating doesPoor forage for lactating does
Little cover for fawnsLittle cover for fawns
Fewer buffer speciesFewer buffer species
Supplemental Feeding:the Other Equalizer
•• Help even out drought effectsHelp even out drought effects Increase deer visibilityIncrease deer visibility
Increase individual productivityIncrease individual productivity•• Fawns/doeFawns/doe•• Body or antler sizeBody or antler size
Increase density (more deer)Increase density (more deer)…… not always a not always a good thing! good thing!
Expensive, but effective in arid regionExpensive, but effective in arid region
Flexibility:adjust grazing
for drought
Predation• Wolves and bears controlled in Alaska and
Yukon to benefit moose populations– Use this manipulation to study predation effects
• Bears and wolves near carrying capacity– Moose densities avg=148/1000km2 (range 45-
417)
• Bears and wolves below carrying capacity– Moose densities avg=663/1000km2 (range 169-
1447)
Predation
• 4 factors influence effect on prey– Ratio of predators to prey
– Vulnerability of prey
– Changes in predator behavior
– Density independent factors
Predation
• Ratio of predators to prey–Higher ratio predators likely to limit
prey species
–1 wolf:200 caribou is stable
–1 wolf:20 moose is stable
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• Fig. 31-7 from text book
Predation• Ratio of predators to prey
–Numerical response of predators • More deer = more food more
coyotes (or wolves, etc.)??–Prey diversity–Alternative prey could remove numerical
response. –Many small mammals may allow coyote
populations to remain high, even if deer decrease
Predation
• Ratio of predators to prey– R values, longevity of prey and predators
• Predators lower reproductive rates and higher survival rates than prey
– Predator swamping• When prey is vulnerable, have many
individuals to limit predator impact• Caribou calves
Predation
• Fig.1 JWM 65:19-24
Predation
• Ratio of predators to prey–Geographic concentrations of
predators• Garbage dumps and bears
–Intrinsic regulation of predators• Territoriality could limit predator
numerical response
Predation• Predator behavior
– Concentration of predation• Success causes predators to focus effort
– Predator learning• Experience more effective techniques
– Predator group facilitation• Groups of predators more successful than
single predator (e.g. wolf packs)